The present invention relates to methods and apparatus for forming servo patterns in substrates for magnetic recording media utilized in high areal, high track density applications, and to magnetic recording media produced thereby. The invention has particular utility in the manufacture of magnetic data/information storage and retrieval media, e.g., hard disks, utilizing very hard surfaced, high modulus substrates such as of glass, ceramic, and glass-ceramic materials.
Magnetic recording media are widely used in various applications, particularly in the computer industry. A portion of a conventional recording medium 1 utilized in disk form in computer-related applications is schematically depicted in FIG. 1 and comprises a non-magnetic substrate 10, typically of metal, e.g., an aluminum-magnesium (Alxe2x80x94Mg) alloy, having sequentially deposited thereon a plating layer 11, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer 12, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer 13, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (xe2x80x9cDLCxe2x80x9d), and a lubricant topcoat layer 15, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium 1, the magnetic layer 13 can be locally magnetized by a write transducer or write head, to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer 13, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (xe2x80x9cCSSxe2x80x9d) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
It is considered desirable during reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head(s) as close to the associated recording surface(s) as is possible, i.e., to minimize the xe2x80x9cflying heightxe2x80x9d of the head(s). Thus a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
Disk drives typically comprise a magnetic head assembly mounted on the end of a support or actuator arm which positions the head radially over the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk surface known as a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially over the disk surface between tracks.
The disk drive must be able to differentiate between tracks on the disk and to center the magnetic head over any particular track. Most disk drives use embedded xe2x80x9cservo patternsxe2x80x9d of magnetically recorded information on the disk. The servo patterns are read by the magnetic head assembly to inform the disk drive of the track location. Tracks typically include both data sectors and servo patterns. Each data sector contains a header followed by a data section. The header may include synchronization information to synchronize various timers in the disk drive to the speed of disk rotation, while the data section is used for recording data. Typical servo patterns are described in, for example, U.S. Pat. No. 6,086,961, the disclosure of which is incorporated herein by reference.
Servo patterns are usually written on the disk during manufacture of the disk drive, after the drive is assembled and operational. The servo pattern information, and particularly the track spacing and centering information, needs to be located very precisely on the disk surface. However, at the time the servo patterns are written, there are no reference locations on the disk surface which can be perceived by the disk drive. Accordingly, a highly specialized device known as a xe2x80x9cservo-writerxe2x80x9d is used during writing of the servo-patterns. Largely because of the locational precision needed, servo-writers are expensive, and servo-writing is a time-consuming process.
One approach (i.e., xe2x80x9cPERMxe2x80x9d disks, manufactured by Sony Corp.) to avoid traditional servo-writing has been to injection mold or stamp servo patterns on a polymer-based substrate disk. A constant thickness layer of magnetic recording material is then applied over the entire disk surface, including the depressions and protrusions of the servo patterns. After all of the constituent layers of the medium have been applied to the disk, a magnetic bias is recorded on the servo patterns. For example, a first magnetic field may magnetically initialize the entire disk at a one setting. Then a second magnetic field, located at the surface of the disk and e.g., provided by the magnetic head of the disk drive, is used to magnetize the protruding portions of the servo patterns relative to the depressions. Because the protrusions are closer than the depressions to the magnetic initialization, the magnetization carried by the protrusions may be different than the magnetization carried by the depressions. When read, the resulting disk servo patterns show magnetic transitions between the depressions and the protrusions.
Meanwhile, the continuing trend toward manufacture of very high areal density magnetic recording media at reduced cost provides impetus for the development of lower cost materials, e.g., polymers, glass, ceramics, and glass-ceramics composites as replacements for the conventional Al alloy-based substrates for magnetic disk media. However, poor mechanical and tribological performance, track mis-registration (xe2x80x9cTMRxe2x80x9d), and poor flyability have been particularly problematic in the case of polymer-based substrates fabricated as to essentially copy or mimic conventional hard disk design features and criteria. On the other hand, glass, ceramic, or glass-ceramic materials are attractive candidates for use as substrates for very high areal density disk recording media because of the requirements for high performance of the anisotropic thin film media and high modulus of the substrate. However, the extreme difficulties encountered with grinding and lapping of glass, ceramic, and glass-ceramic composite materials have limited their use to only higher cost applications such as mobile disk drives for xe2x80x9cnotebookxe2x80x9d-type computers.
Presently, media anisotropy is achieved by circumferentially polishing (xe2x80x9cmechanically texturingxe2x80x9d) Al alloy substrates with NiP plating layers using a diamond or other relatively hard abrasive in slurry form dispensed on an absorbent and compliant polishing pad or tape. Sub-micron flyability (e.g.,  less than 0.5 xcexcinch) of the recording transducer or head over a is a requirement for obtainment of very high areal density recording media. However, attempts to achieve the requisite surface topography on glass, ceramic, or glass-ceramic composite substrates have been unsuccessful due to their extreme hardness (e.g., glass substrates have a Knoop hardness greater than about 760 kg/mm2 compared with about 550 kg/mm2 for Al alloy substrates with NiP plating layers). In addition, the low flowability and extreme hardness of these substrate materials effectively precludes formation of servo patterns in the surfaces thereof by injection molding or stamping, as has been performed with polymer-based substrates.
In view of the above, there exists a need for improved methodology and means for providing disk substrates for magnetic recording media, which substrates are constituted of very hard materials, with at least one surface of requisite topography for enabling operation with flying head read/write transducers/heads operating at very low flying heights and with servo patterns provided therein, as by embossing. More specifically, there exists a need for an improved means and methodology for embossing a pattern, i.e., a servo pattern, in a surface of a substrate for a magnetic recording medium, comprised of a glass, ceramic, or glass-ceramic composite material. In addition, there exists a need for an improved, high areal density magnetic recording medium including a high hardness, high modulus substrate having a servo pattern integrally formed therewith, as by embossing.
The present invention addresses and solves problems and difficulties attendant upon the use of very hard materials, e.g., of glass, ceramic, or glass-ceramic, as substrate materials in the manufacture of very high areal density magnetic recording media, while maintaining full capability with substantially all aspects of conventional automated manufacturing technology for the fabrication of thin-film magnetic media. Further, the methodology and means afforded by the present invention enjoy diverse utility in the manufacture of various other devices and media requiring formation of patterned surfaces by embossing of high hardness materials.
An advantage of the present invention is an improved method of manufacturing a magnetic recording medium including a patterned surface.
Another advantage of the present invention is an improved method of manufacturing a magnetic recording medium including a high modulus substrate having a servo-patterned glass or glass-like layer formed on a surface thereof.
Yet another advantage of the present invention is an improved magnetic recording medium including an embossed servo pattern formed therein and capable of operation with transducer heads at sub-micron flying heights.
Still another advantage of the present invention is an improved magnetic recording medium comprised of a high modulus substrate including a sintered glass or glass-like layer formed thereon and having a servo pattern formed therein.
A further advantage of the present invention is a stamper having a hydrophobic surface for embossing a servo pattern in the surface of a hydrophilic sol-gel layer formed on a surface of a high modulus substrate for a magnetic recording medium.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a method of manufacturing a magnetic recording medium, comprising the sequential steps of:
(a) providing a non-magnetic substrate for a magnetic recording medium, the substrate including at least one major surface;
(b) forming a layer of a sol-gel on the at least one major surface of the substrate;
(c) forming a pattern in an exposed surface of the layer of the sol-gel; and
(d) converting the layer of the sol-gel to a glass or glass-like layer while preserving the pattern in an exposed surface of the glass layer.
According to embodiments of the present invention, step (a) comprises providing a disk-shaped, high modulus substrate having a pair of major surfaces and comprised of a glass, ceramic, or glass-ceramic material; step (b) comprises forming the layer of the sol-gel by spin coating a solution of the sol-gel on the at least one major surface of the substrate; and step (c) comprises embossing a servo pattern in the exposed surface of the layer of the sol-gel by applying thereto a surface of a stamper, the surface of the stamper including a negative image pattern of the servo pattern.
In accordance with embodiments of the present invention, step (b) comprises forming a layer of a hydrophilic sol-gel on the at least one major surface of the substrate; and step (c) comprises embossing utilizing a stamper wherein at least the patterned surface thereof is formed of a hydrophobic material.
According to particular embodiments of the invention, step (c) comprises utilizing a stamper wherein at least the patterned surface thereof is formed of a hydrophobic polymeric material; e.g., an amorphous thermoplastic material selected from polycarbonates, polyetherimides, polypropylenes, and polyethylenes; or step (c) comprises utilizing a stamper having a main body comprised of a first metal and the patterned surface thereof is formed of a second metal, carbon (C), or a hydrophobic polymer e.g., the main body is comprised of nickel (Ni) and the patterned surface thereof is formed of platinum (Pt), carbon (C), or a sputtered hydrophobic polymer.
In accordance with embodiments of the present invention, step (d) comprises sintering the layer of sol-gel at an elevated temperature; and step (b) comprises forming a layer of a sol-gel comprising a porous layer of SiO2 containing water and at least one solvent in the pores thereof, wherein step (d) comprises converting the layer of sol-gel to the glass or glass-like layer by driving out the water and the at least one solvent from the pores by sintering the layer of sol-gel at a temperature of from about 300 to above about 1000xc2x0 C.
According to embodiments of the present invention, the method further comprises the step of:
(e) forming a stack of thin film layers over the exposed surface of the glass or glass-like layer, the stack of layers including at least one ferromagnetic layer.
Another aspect of the present invention is a magnetic recording medium, comprising:
(a) a non-magnetic substrate having at least one major surface;
(b) a sintered glass or glass-like layer formed on the at least one major surface, the sintered glass or glass-like layer including an upper surface having an embossed pattern formed therein; and
(c) a stack of thin film layers formed over the upper surface of the sintered glass or glass-like layer, the stack of layers including at least one ferromagnetic layer.
In accordance with embodiments of the present invention, the non-magnetic substrate (a) is disk-shaped with a pair of major surfaces and comprised of a high modulus material selected from glass, ceramic, and glass-ceramic materials; and the sintered glass or glass-like layer (b) is derived from a sol-gel layer and includes an embossed servo pattern formed therein.
Yet another aspect of the present invention is a stamper for embossing a servo pattern in a surface of a layer of a hydrophilic sol-gel formed on a surface of a substrate for a magnetic recording medium, comprising:
(a) a main body having an embossing surface including a negative image of the servo pattern; and
(b) means for facilitating release of the embossing surface of the stamper from the surface of the layer of sol-gel subsequent to embossing of the servo pattern.
According to particular embodiments of the present invention, the main body and the embossing surface of the stamper are formed of a hydrophobic polymeric material, e.g., an amorphous thermoplastic material selected from polycarbonates, polyetherimides, polypropylenes, and polyethylenes; whereas, according to other particular embodiments of the present invention, the main body is formed of a first metal and the embossing surface is formed of a second metal, carbon, or a hydrophobic polymer, e.g., the first metal is nickel and the embossing surface is made of platinum, carbon, or a sputtered hydrophobic polymer.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.